Diatoms of North AmericaThis spring we celebrated the 50th anniversary of the “Diatom Clinic”, which was started by then graduate student Gene Stoermer at the Iowa Lakeside Laboratory in 1963. Our class of 10 students arrived from all over the country (Alaska, Arizona, Arkansas, California, Colorado, Louisiana, Maryland, Minnesota, Ohio), and with varying backgrounds (undergraduates, recent graduates, graduate students, professors, professionals) to explore and learn about the world of diatoms. Mark Edlund and Marina Potapova led the charge during this extraordinary and enlightening four-week stay on the shores of West Lake Okoboji.
Dr. Evelyn Gaiser from Florida International University visited Lakeside Lab during the class and gave several lectures and a public talk entitled "From Poutine to Boiled Peanuts: Unraveling the Biogeography of Karstic Wetland Diatoms from Canada to the Tropics". Evelyn is an alumnus of the 1989 Diatom Class, the last class taught by Dr. Charlie Reimer, and did her M.S. research at Lakeside on epizooic diatoms of the Iowa Great Lakes region.
In addition to a rigorous workload, this year’s class took on an exciting project examining a population of Diatoma vulgaris from East Lake Okoboji that had recently undergone sexual reproduction. Shallow epilithic samples collected from East Lake Okoboji, Dickinson County, Iowa had highly variable populations of Diatoma including Diatoma vulgaris and its varieties, linearis and breve. A bi-modal distribution of valve lengths was observed for the Diatoma varieties ranging from 21 to 88 µm. Initially the length distribution was dominated by an abundance of valves between 60-70 µm and a smaller population with lengths between 30-40 µm. After three weeks the populations were resampled and the bi-modal distribution shifted to dominance by the 30-40 µm valve length group. Across the length range valves showed little variation in breadth and costae density, so we further examined the morphology using sliding landmarks to describe valve shape. Multivariate analysis of the sliding landmarks yielded a morphological trajectory axis where valves with a narrow middle and long capitate ends were reduced to valves with a central widening and rounded subrostrate ends. When valve shapes along this axis were compared with valve diminution, a decrease in valve length explained 93% of the variation in the change from a narrow middle with capitate ends to the central widening and rounded ends. These data indicate that our collections represent a single taxon, which we determine to be Diatoma vulgaris, that the population had recently undergone sexual reproduction, and that within the size and shape variation of this single species many of its described varieties can be accommodated.
David Burge and Natalie Hoidal will be giving an oral presentation of the class project at the 2013 North American Diatom Symposium in Maine this August.
